Genetics of Muscle Disease

Nowak, Kristen J.; Lamont, Phillipa; Laing, Nigel G.

doi:10.1002/9781118635469.ch4

Cited by 2 publications

References 95 publications

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SMN deficiency induces an early non-atrophic myopathy with alterations in the contractile and excitatory coupling machinery of skeletal myofibers in the SMNΔ7 mouse model of spinal muscular atrophy

Berciano,

Gatius,

Puente-Bedia

et al. 2024

Preprint

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Spinal muscular atrophy (SMA) is caused by a deficiency of the ubiquitously expressed survival motor neuron (SMN) protein. The main pathological hallmark of SMA is the degeneration of lower motor neurons (MNs) with subsequent denervation and atrophy of skeletal muscle. However, increasing evidence indicates that low SMN levels not only are detrimental to the central nervous system but also directly affect other peripheral tissues and organs, including skeletal muscle. To better understand the potential primary impact of SMN deficiency in muscle, we explored the cellular, ultrastructural, and molecular basis of SMA myopathy in the SMNΔ7 mouse model of severe SMA at an early postnatal period (P0-7) prior to muscle denervation and MN loss (preneurodegenerative [PND] stage). This period contrasts with the neurodegenerative (ND) stage (P8-14), in which MN loss and muscle atrophy occur. At the PND stage, we found that SMNΔ7 mice displayed early signs of motor dysfunction with overt myofiber alterations in the absence of atrophy. Focal and segmental lesions in the myofibrillar contractile apparatus were noticed in myofibers. These lesions were observed in association with specific myonuclear domains and included abnormal accumulations of actin-thin myofilaments, sarcomere disruption, and the formation of minisarcomeres. The sarcoplasmic reticulum and triads also exhibited ultrastructural alterations, suggesting decoupling during the excitation-contraction process. Finally, changes in intermyofibrillar mitochondrial organization and dynamics, indicative of mitochondrial biogenesis overactivation, were also found. Overall, our results demonstrated that SMN deficiency induces early and MN loss-independent alterations in myofibers that essentially contribute to SMA myopathy. This strongly supports the view of an intrinsic alteration of skeletal muscle in SMA, suggesting that this peripheral tissue is a key therapeutic target for the disease.Graphical summarySchematic representation of the main cellular and ultrastructural changes occurring intibialis anterior(TA) myofibers of the SMNΔ7 mouse model of severe SMA during the pre-neurodegenerative stage (PND, P0-P7). See that the PND stage is characterized by the absence of MN loss and muscular atrophy but, SMN deficient myofibers display multiple alterations. Observe the early impact of low SMN levels on sarcoplasmic reticulum and triads, myofibril contractile cytoskeleton, and intermyofibrillar mitochondria. Notice that all alterations are associated with a specific myonuclear domain. Changes in mRNA levels of different genes involved in myogenesis and mitochondrial biogenesis are also shown compared to age-matched WT animals. Figure created withBioRender.com.

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SMN deficiency induces an early non-atrophic myopathy with alterations in the contractile and excitatory coupling machinery of skeletal myofibers in the SMNΔ7 mouse model of spinal muscular atrophy

Berciano,

Gatius,

Puente-Bedia

et al. 2024

Preprint

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Immunohistochemistry of sarcolemmal membrane-associated proteins in formalin-fixed and paraffin-embedded skeletal muscle tissue: a promising tool for the diagnostic evaluation of common muscular dystrophies

et al. 2017

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BackgroundThe analysis of fresh frozen muscle specimens is standard following routine muscle biopsy, but this service is not widely available in countries with limited medical facilities, such as Thailand. Nevertheless, immunohistochemistry (IHC) analysis is essential for the diagnosis of patients with a strong clinical suspicion of muscular dystrophy, in the absence of mutations detected by molecular genetics. As the successful labelling of sarcolemmal membrane-associated proteins in formalin-fixed and paraffin-embedded (FFPE) muscle sections using IHC staining has rarely been described, this study aimed to develop a reproducible IHC method for such an analysis.MethodsThirteen cases were studied from the files of the Department of Pathology, Mahidol University. Diagnoses included three Duchenne muscular dystrophy (DMD), one Becker muscular dystrophy (BMD), one dysferlinopathy, and several not-specified muscular dystrophies. IHC was performed on FFPE sections at different thicknesses (3 μm, 5 μm, and 8 μm) using the heat-mediated antigen retrieval method with citrate/EDTA buffer, followed by an overnight incubation with primary antibodies at room temperature. Antibodies against spectrin, dystrophin (rod domain, C-terminus, and N-terminus), dysferlin, sarcoglycans (α, β, and γ), and β-dystroglycan were used. Frozen sections were tested in parallel for comparative analysis.ResultsAntibodies labelling spectrin, dystrophin (rod domain and C-terminus), dysferlin, sarcoglycans (α, β, and γ), and β-dystroglycan clearly exhibited sarcolemmal staining in FFPE sections. However, staining of FFPE sections using the antibody directed against the N-terminus of dystrophin was unsuccessful. The absence of labeling for dystrophins and dysferlin in FFPE sections was documented in all three DMD patients and the dysferlinopathy patient. The BMD diagnosis could not be made using IHC in FFPE sections alone because of a lack of staining for the dystrophin N-terminus, indicating a limitation of this method.ConclusionsWe developed a reliable and reproducible IHC technique using FFPE muscle. This could become a valuable tool for the diagnosis of some muscular dystrophies, dystrophinopathies, sarcoglycanopathies (LGMD2D, LGMD2E, and LGMD2C), and dysferlinopathy, especially in situations where the analysis of fresh frozen muscle samples is not routinely available.

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Genetics of Muscle Disease

Cited by 2 publications

References 95 publications

SMN deficiency induces an early non-atrophic myopathy with alterations in the contractile and excitatory coupling machinery of skeletal myofibers in the SMNΔ7 mouse model of spinal muscular atrophy

SMN deficiency induces an early non-atrophic myopathy with alterations in the contractile and excitatory coupling machinery of skeletal myofibers in the SMNΔ7 mouse model of spinal muscular atrophy

Immunohistochemistry of sarcolemmal membrane-associated proteins in formalin-fixed and paraffin-embedded skeletal muscle tissue: a promising tool for the diagnostic evaluation of common muscular dystrophies

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